fix(menubar): improve user avatar display logic

- Add null safety checks for user object
- Use optional chaining for safer property access
- Add fallback for empty email/name values

src/components/Menubar/Menubar.tsx

@@ -48,14 +48,16 @@ export function Menubar() {
           <Avatar
             sx={{
               bgcolor: stringToColor(
-                user.family_name ? user.family_name : user.email
+                (user && user.family_name) ? user.family_name : 
+                (user && user.email) ? user.email : 
+                ''
               ),
             }}
             sizes="large"
           >
-            {user.name && user.family_name
+            {user?.name && user?.family_name
               ? `${user.name[0]}${user.family_name[0]}`
-              : user.email[0]}
+              : user?.email?.[0] ?? ''}
           </Avatar>
         </div>
       </header>